The protoss possess telepathy universally. Indeed, they are so proficient at it that during the Aeon of Strife, protoss could even prevent others from gaining access to their minds without technological devices.[4] Protoss are able to read the minds of terrans with ease, but possess enough self control to not read such thoughtstreams.

The Khala-following protoss can/could not completely hide their thoughts from each other, but the ability can still be used to a degree.[5] The amount of privacy in a conversation is up to the protoss involved in it and their level of psionic control, able to fine-tune their thoughts to such an extent that "mental spikes" may be generated, causing pain to their recipients.[6] Khalai were able to communicate wordlessly due to the nature of the Khala.[7]

The range of protoss telepathy is unknown to Dominionscientists, but it is not infinite. Psychic boosters are used for ship-wide telepathic broadcasts, while psi-link spires are used for interstellar psionic communication.[8]Psi links allow protoss to communicate over the mental chaos of battle, and art often outfitted into their suits.[9]

Protoss who do not follow the Khala (such as the Dark Templar) can completely shutter their minds to other protoss.[5]

Terrans have the potential to become a potent psionic race in only a few generations, although psychic abilities are currently rare.[2] Terran psychic power is measured on the Psionic Index; most terrans have a PI of 2 or less.[1] The inner thoughts of terrans rarely correspond to how they present themselves to those around them.[10]

A few terran individuals possess telepathy. Most of these individuals become ghosts, who generally have a PI of 5 or 6.[1] However, the degree of telepathy varies; the ability to sense surface thoughts is seemingly universal for such individuals[6] although to directly read an individual's thoughts is not as common. Reading thoughts unintentionally is generally a given for telepaths[1] and some are never able to completely filter external thoughts. This can create "feedback loops", where a person's thoughts is mirrored by the telepath. External fear becomes the telepath's fear, external anger becomes the telepath's anger, etc.[11] These thoughts are even capable of manifesting in the dreams of a telepath[12] and dreams, or the lack of them, can be read directly.[10] However, with enough training, it is not impossible for a terran to prevent him/herself from doing so.[1]

In addition, non-telepaths, with enough willpower, can keep their thoughts to themselves.[13] Some telepaths can resist mind-reading attempts[14] and/or generate false surface thoughts in order to avoid suspicion. Dominion regulations prohibit telepaths in their service from reading officials' minds without just cause—an individual's rank plays a role in this.[10]

Terran telepaths have been observed sending telepathic messages[15] although without the clarity displayed by the protoss.[5] Electronics, particularly around the head region, was known to interfere with telepathy.[1]

Psychics with a PI value of less than 5 have difficulty creating telepathic messages or creating "mental maps".[15]

The zerg are entirely telepathic, but in a different manner to the protoss. While each protoss individual is his/her own self, the zerg utilized a mental hierarchy, with the Overmind at the top, moving down to cerebrates, overlords, queens, and steadily down to lesser strains.[16] These strains are capable of 'speech',[5] but are incapable of ignoring the directives of higher strains.[2] Although the Queen of Blades has taken the role of the Overmind at the top of the zerg hierarchy, the process remains the same.[5]

To date, no thoughts of lesser strains have ever been known to be read by a protoss or terran telepath. The only known exception is Jim Raynor, who was able to hear the zerg 'speaking' whilst on Char. This was due to Kerrigan wielding her telepathy clumsily, and filtering her unwanted thoughts into Raynor whilst she came to accept who and what she had become. The protoss Zeratul was aware of this, but could not hear the zerg's thoughts.[16] During a mission to Altara, Nova was able to sense a mass of zerg thought that corresponded to approaching zerg, but couldn't sense the individual elements of the thought mass.[10]

Higher strains are a different story however, as Zeratul was able to communicate with the cerebrateZasz via telepathy before assassinating the creature. Upon doing so, his mind connected with that of the Overmind, their thoughts being exchanged.[16] The Overmind learnt of the location of the protoss homeworld of Aiur,[17] while Zeratul learnt of the zerg's origins and goal of assimilating the protoss race.[18] The emotions of higher strains can be mirrored by lower strains, akin to a feedback loop.[6]

↑Overmind: "Yet shall their overweening pride be their downfall. For when the assassin Zeratul murdered Zasz, his mind touched with mine, and all his secrets were made known to me. I have taken from his mind the secret location of Aiur, the Protoss Homeworld." StarCraft. Vivendi Games. Level/area: Eye for an Eye (in English). 1998.

↑Tassadar: "Zeratul, perhaps the time has come to tell our friends of the foe we face."Zeratul: "Indeed. When I slew the Cerebrate on Char, I touched briefly with the essence of the Overmind. In that instant, my mind was filled with its thoughts, and I tell you now our worst fears have come true. The Zerg were indeed created by the ancient Xel'Naga, the same beings that empowered us in our infancy. But the Overmind grew beyond their constraints, and has at last come to finish the experiments they began so long ago." StarCraft. Vivendi Games. Level/area: Shadow Hunters (in English). 1998.